The present invention relates to an apparatus and method to measure material resistance in nonferrous materials. More specifically, the invention relates to an apparatus and method to non-destructively measure resistance and changes in resistance in nonferrous materials using remote field eddy current technology.
Material analysis at nuclear facilities, such as nuclear electrical generating stations, is becoming increasingly critical to plant and personnel safety. Special materials are often selected for use in nuclear facilities to solve varied design problems. The special materials selected must often withstand forces developed from temperature fluctuation, radiation exposure, pressure, and other factors.
Failure to detect problems in these special materials can have varied consequences. These consequences include causing a station forced outage, equipment malfunction, material damage, radiation exposure to workers and extended maintenance outages. The potential severe consequences to safety as well as economic concerns from shutting down a nuclear electrical generating station necessitate minimization of material defects. Consequently, accurate and reliable analysis techniques are needed to ensure material viability used in nuclear operations.
Exposure to radiation causes certain materials to undergo changes in atomic structure and composition. A typical example of this is inclusion of hydrogen into non-ferrous materials. The inclusion of hydrogen into nonferrous materials can result in a loss of material ductility as well as changes to the materials electrical resistance.
The ductility of materials is often relied on to counteract the effects of a design basis accident, such as a loss of coolant accident, seismic event or pressure transient. When possible, ascertaining hydrogen content in a material allows maintenance personnel to assess the necessity of replacing or retiring a material from service. Thus, maintenance personnel use these assessments to verify conformance of installed equipment to original design specifications.
One of the most important components in a nuclear electrical generating station is a nuclear fuel assembly. Nuclear fuel assemblies usually consist of uranium based fuel pellets surrounded by a protective cladding. The cladding typically used is a nonferrous material, usually a type of zirconium alloy. The use of zirconium alloys provides both mechanical and chemical protection for the fuel pellets. Cladding materials must have excellent corrosion resistance, ductility, and the ability to withstand wide variations in temperature. In an operating nuclear electrical generating station, the cladding undergoes intense exposure to radiation throughout its service life. This intense exposure can be for prolonged cycles, in some instances 24 months between maintenance periods. When exposed this high radiation, zirconium alloys accumulate hydrogen into the alloy matrix.
To quantify the amount of hydrogen in a material used in a high radiation area, current practice requires removal of the material from service. Following removal from service, the material is placed into a facility known as a xe2x80x9chot cellxe2x80x9d. While in the xe2x80x9chot cellxe2x80x9d, the material is destructively tested to determine the hydrogen content.
Current destructive measurement processes can accurately measure the amount of hydrogen in the material, however certain drawbacks are readily apparent. Current processes require removal of the material from service and shipping to a specially equipped xe2x80x9chot cellxe2x80x9d laboratory. When the material is destructively tested, the material is no longer available for use. Furthermore, the destructive testing generates waste that must be disposed in a proper manner, increasing material handling and storage costs.
Accordingly, there is a need to non-destructively measure resistance changes in materials, such as nuclear fuel rod cladding.
The invention described herein achieves the above needs through the apparatus and method described.
The present invention provides a method of measuring an electrical resistance change in a nonferrous material. The method includes the steps of: providing a nonferrous material, inducing a magnetic field from the nonferrous material, measuring the remote magnetic field of the nonferrous material and comparing the measured remote field to a standard.
The present invention provides a method of measuring the electrical resistance of a nonferrous material. This method for measuring the electrical resistance of a material includes the steps of providing a nonferrous material; inducing a magnetic field from the nonferrous material; measuring the remote magnetic field of the nonferrous material and calculating the resistance of the nonferrous material.
The present invention also provides an apparatus for measuring a resistance or resistance change in a nonferrous material using remote field eddy current technology. The apparatus includes a receiving coil circuit having an eddy current instrument connected to a Remote Field Testing (RFT) receiving coil. The apparatus also includes an Outside Diameter (OD) circuit comprising an amplifier connected to an Outside Diameter Remote Field Testing (OD RFT) exciter coil arrangement and a frequency generator.